1. Field
The following description relates to encoding and decoding of video signal, more specifically to a method for selecting content adaptive coding mode that can improve image quality by initially selecting a block having improper motion information by using a local dispersion value in the update process of motion compensated temporal filtering (MCTF) and then converting and coding a portion that is difficult to predict into a coding mode in the screen by using the block.
2. Description of the Related Art
Multimedia technologies are required in various sectors due to the recent development of hardware and increased demand by users. Such various user demands have made the use of images increasingly diverse so that it is required to develop a scalable video codec (SVC) technology that allows an image technology to use a single original image in various applications, from TV to DMB and personal terminals, with various qualities, spatial resolutions and frame ratios.
The SVC is divided mainly into space scalability, quality scalability and time scalability. Among them, motion compensated temporal filtering (MCTF) using a lifting scheme corresponding to the space scalability has a basic role in supporting the space scalability of the SVC.
Particularly, the MCTF serves to remove redundancy between frames in addition to providing time scalability by using a wavelet method, and the wavelet filtering is applied by using the lifting scheme.
FIGS. 1A and 1B show circuits of MCTF using a lifting scheme and its reverse conversion.
Referring to FIGS. 1A and 1B, the lifting scheme mainly goes through two steps. First, as shown in FIG. 1A, motion information of images has to be found in a prediction process, and then a high frequency band image H is generated by using the motion information. Then, in the second step, a low frequency band image L is generated in an update process by using the high frequency band image, which is generated in the first step. During the two steps, the energy of the images is transferred to as low a frequency band as possible, and low energy is maintained in a high frequency band so as to increase the coding efficiency.
As shown in FIG. 1B, in the reverse conversion, it is also possible to restore the original without new additional information.
However, a disadvantage of the MCTF is that proper motion information can not be found as the step increases. That is, referring to the coding structure of 5/3 tap wavelet MCTF shown in FIG. 2, it can be seen that the time interval between the original image and its reference image becomes wider as the steps t-L1 to t-L3 progress, reducing the relevancy between the images.
As such, an effect of a new object appearing or disappearing may not allow proper motion information to be found, and thus the energy to be transferred to the low frequency band may still remain in the high frequency band, thereby lowering the image quality. Moreover, as the step of the MCTF progresses, the deterioration of the image quality may be accumulated over a period of time, making residual image in the image.
To solve these problems, an update process may be omitted so that the accumulation of such noise is prevented. However, such omission of update may cause the deterioration of power signal-to-noise ratio (PSNR). Such effect is caused by the fact that high frequency band information, which is required for restoring, is omitted due to the omission of update.
To solve this problems of MCTF, a content adaptive MCTF update process may be used as a way to reduce the noise by setting a local dispersion value as a critical value for update.
Another consideration to be taken in the update process of the MCTF using the motion information is multiple updates in a pixel that is referenced multiple times. That is, in the update process of generating a low frequency band by using a high frequency band, the reverse direction of motion information used for generating the high frequency band is used, but this may make multiple updates to be performed in one pixel.
Although the content adaptive MCTF update process may reduce the noise by setting the critical value, it can not prevent multiple updates from being performed in one pixel.
Meanwhile, a covered pixel detection algorithm is used to solve the aforementioned problem, and this may prevent multiple updates from occurring and prevent an update from being performed several times in one pixel by selecting pixels that are connected to one another by executing a coding process in the screen in connection with a block having improper motion information.